Welding fixture



Aug. 18, 1942 H. T. PLATZ WELDING FIXTURE Filed March 31, 1941 14Sheets-Sheet 1 non mnm m on mvm v INVENTOR. HENRY THOMAS PLATZ ATTORNEYSH. T. PLATZ WELDING FIXTURE Aug. 18, 1942.

Filed March 31, 1941 14 Sheets-Sheet 2 m: N: wo .om,

INVENTOR. HENRY THOMAS PLATZ ATTORNEYS Aug. 18, 1942. p z

WELDING FIXTURE Filed March 31, 1941 14 Sheets-Sheet 3 INVENTOR.

HENRY THOMAS PLATZ BY I46 1 43 44 FG.5.

7 \47 MTTORNEYQ Aug. 18, 1942.

H T. PLATZ WELDING FIXTURE;

Filed March 31, 1941 14 Sheets-Sheet 4 I NV EN TOR.

||ll llll|lllllllllkll B HENRY THOMAS PLATZ ATTORNEY Aug. 18, 1942.

H. T. PLATZ WELDING FIXTURE Filed March 31, 1941 14 Sheets-Sheet 5INVENTOR. HENRY THOMAS PLATZ 1 I" 'WY ATTORNEYS Aug. 18,1942. H. T.PLATZ 2,293,169

WELDING FIXTURE Filed March 31, 1941 14 Sheets-Sheet 6 FIG.I8.

INVENTOR.

BY I HENRY THOMAS PLATZ ATTORNEYS Aug. 18, 1942. H. T. PLATZ WELDINGFIXTURE Filed March 31, 1941 1-4 Sheets-Sheet 7 Il -l Ill/Ill)- aiEJJJJ-a mz INVENTOR.

HENRY THOMAS PLATZ ATTORNE Aug. 18, 1942. PLATZ 2,293,169

WELDING FIXTURE Filed March 31, 1941 14 Sheets-Sheet B INVENTOR.

HENRY THOMAS PLATZ ATTORNEYS:

Aug. 18, H- T- WELDING FIXTURE Filed March 31, 1941 14 Sheets-Sheet 9INVENTOR.

HENRY THOMAS PLATZ NVN 1 ATTORNEY NVN ////l l/ 1/ ll Aug. 18,1942.

H. T. PLATZ WELDING FIXTURE Filed March 31, 1941 14 Sheets-Sheet 10ATTORNE S Aug. 18, 1942. H. 'r. PLATZ WELDING FIXTURE Filed'larc'h 31,1941 14 Sheets-Sheet ll nNdE AS PLA T Z ATTORNEY mm mom 3 w B: U W 3.. a71? a.

1942- H. PLATZ 7 2,293,169

WELDING FIXTURE Filed March 31, 19:41 14 Sheets-Sheet 12 FIG.32.

FIG.25.

INVENTOR. HENRY THOMAS P LATZ ATTORNEY Aug. 18, 1942. H. T. PLATZWELDING FIXTURE Filed March 31, 1941 14 Sheets-Sheet l3 mwdE mmmm- NON I1 IL L11 N2 H X m A E H n m: a wmdc INVENTOR. HENRY THOMAS PLATZ W+ATTORNEYS Patented Aug. 18, 1942 UNITED STATES PATENT OFFICE WELDINGFIXTURE Henry Thomas Platz, Detroit, Mich., assignor to BriggsManufacturing Company, Detroit, Mich,

a corporation of Michigan Application March 31, 1941, Serial No. 386,160

23 Claims.

This invention relates generally to welding apparatus and refers moreparticularly to improvements in fixtures for use in conjunction withwelding equipment.

It is one of the principal objects of this invention to provide awelding fixture which is thoroughly automatic in operation and which iscapable of welding the work at a plurality of points in the minimumlength of time.

Another object of this invention is to provide a fixture having aplurality of groups of welders supported above a conveyer track inspaced relation to each other in the direction of length of the trackand having work supporting carriages movable along the track by a stepby step movement to successively register the work on the carriageswiththe groups of welders.

Another object of this invention is to provide means operable during theintervals of rest of the carriages to simultaneously lift the carriagesofi the track to position the work on the carriages in operativerelation to the welders.

Another feature of this invention is to provide means responsive tomovement of the work into operative relationship with the welders toeffect an operation of the welders and thereby weld the work at aplurality of points.

Still another feature of the present invention is to provide a fixtureof the above type wherein each group of welders is operatedindependently of one another and wherein the operating means for eachgroup of welders is initiated by the carriages as the latter are raisedto their uppermost positions with respect to the welders. By providingindependent operating means for the several groups of welders, one groupmay possess a different welding cycle than another group, and this isadvantageous in cases where the thickness of the metal of certain partsof the work to be 5 track during the intervals of rest of the carriageson the track and having additional means for transferring a carriagefrom the delivery end of the conveyer track to a loading station.

Still another object of the present invention is to provide indexingmechanism for the carriages on the conveyer track including an electriccircuit having switches connected in series therein and adapted to berespectively closed by the carriages as the latter assume positions atthe entrant end of the conveyer track and at the loading station.

Still another object of this invention is to position the carriages onthe conveyer track with the adjacent ends of the carriages abutting oneanother so that motion transmitted to the carriage at the entrant end ofthe track effects a corresponding movement of the remaining carriages onthe track.

A still further object of this invention consists in connecting a switchin series in the indexing circuit and providing means for closing theswitch in response to return movement of the carriages to positions onthe track. With this arrangement, the indexing mechanism is preventedfrom operating until the carriages have assumed positions on the track.

Another object of this invention is to provide a cross conveyer betweenthe delivery end of the welding conveyer track and the loading stationfor transferring the carriages leaving the delivery end of the weldingconveyer track to the loading station and to further provide means formoving the transfer carriagerendered operative by a carriage as thelatter is movedfrom the dewelded is different from the thickness of thelivery end of the conveyer track to a position on metal or other partsof the work to be welded.

Another object of this invention which contributes materially toobtaining the above advantage consists in providing a fixture whereineach group of welders comprises a plurality of sets of welders which areoperated independently of one another to weld the work on the carriagesas the latter are moved to their uppermost positions with respect to thewelders.

the cross conveyer.

Another advantageous feature of the present invention is to provide aloading conveyer extending from the loading station to a position.adjacent the entrant end of the welding conveyer track and to connectthe delivery end of the loading conveyer to the entrant end of thewelding conveyer by a cross conveyer.

A still further object of the present invention Still another feature ofthe present invention is to provide means rendered operative by moveisto provide a fixture having means for returning the carriages topositions on the track and having means for rendering the operation ofthe last named means inoperative until each group or set of welders hascompleted its welding cycle.

ment of a carriage on the cross conveyer from the delivery end of theloading conveyer to move the cross conveyer in a direction to positionthe carriage in registration with the entrant end of the weldingconveyer.

ing an electric circuit having a pair of switches connected in seriestherein and respectively closecl'by a carriage movable onto the crossconveyer from the delivery end of the loading conveyer and by a carriagemovable on oi the cross conveyer onto the entrant end of the weldingconveyor. The arrangement is such that the cross conveyer is preventedfrom operation un til the carriage in registration with the entrant endof the welding conveyor is moved onto the latter.

A still further object of the present invention is to provide means forretarding movement of the carriages on the weldingconveyer tracl; at theends of each indexing strolre and to provide means for positivelyarresting the carriages in registration with the lifting means.

The foregoing as well as other objects will he made more apparent asthis description proceeds, especially when considered in connection withthe accompanying drawings, wherein:

Figure l is a wiring diagram of the fixture forming the subject matterof this invention and diagrammatically illustrates a part of the fixturein plan view;

Figure 2 is a fragmentary side elevational view of a part of the fixtureforming the subject matter of this invention;

Figure 3 is a semi-diagrammatic view partly in section illustrating apart of the welding system embodied in the fixture;

Figure i is a plan 'view of the construction shown in Figure 3;

Figure 5 is a, sectional view through the welder control unit shown inFigure i;

Figure 6 is a fragmentary plan view. of the loading conveyor embodied inthe fixture;

Figure 'l is a side elevational view of the loading conveyor shown inFigure 6 and having certain parts broken away for the sake of clear- 7ness.

Figure 8 is a sectional view taken substantially on the line fi-d ofFigure 6;

Figure 9 is a fragmentary side elevational view of the welding conveyerembodied in the fixture;

Figure 10 is a cross sectional view taken sub lc-lc of Figure Figure 17is a sectional view taken on the line l1|'| of Figure 15; I

Figure 18 is a sectional view taken on the line 18-48 of Figure 17;

aasaiee Figure 19 is a iragmentary sectional view illustrating the latchassociated with the welding conveyer;

section of the operating means for the cross conveyor shown in Figure21;

Figure 27 is a sectional view taken on the line 2-3El of Figure 26; I

Figure 28 is a sectional view taken on the line of Figure 23;

Figure 29 is an end elevational view showing one of the brakes of thecross conveyer;

Figure 3G is a side elevational view showing the unloadingmeans at thedelivery end of the welding conveyer;

Figure 31 is a sectional view taken on the line 35-2-3? of Figure 30;and

Figure 32 is a sectional view through the bumper provided at thedelivery end of the welding conveyor.

Although many of the principles of this invention may be advantageouslyused in instances where it is desired to produce a maximum numher ofwelds in the minimum time interval, nevertheless, in order to illustratethe invention, I have selected a fixture especially designed for use inmass production of vehicle bodies. More particularly; the fixtureillustrated herein is adapted to weld the several parts of a vehicle:door assembly together to form a unitary construction and accomplishesthis result in a relativelyshort time interval.

In general, the fixture embodies a plurality of welders arranged ingroups at a plurality of stations and adapted to operate simultaneouslyon fioor assemblies corresponding in number to the number of weldingstations. As will be presently set iorth, the weldersat each station arepredeterminedly arranged to weld dlfierent portions of the floorassemblies together, and the latter are successively moved intooperative relation to the welders at :each station so that when thefloor assemblies leave the last welding station, all of the variousparts of the floor assemblies are permanently secured together.

With the above in mind, reference will now be made to the drawingswherein it will be noted that the fixture selected herein for thepurpose of illustrating the invention comprises a loading conveyer 35and a welding conveyor 36. The two conveyors extend parallel to oneanother and are positioned in lateral spaced relationship.

.Upon reference to Figures 1, 2, Gland 7, it will I be noted that eachconveyer comprises a pair of laterally spaced longitudinally extendingtracks 31 secured to suitable frame structure and adapted to support aplurality of Work supporting carriages 38. The carriages 38 have arolling engagement with the tracks and are moved by a step by stepmovement along their respective tracks in a manner to be more fullyhereinafter set forth.

The tracks 31. of each conveyor are of equal length and the delivery end39 of the loading cqnveyer track 31' is connected to the entrant veyer41.

end 48 of the welding conveyer by a transfer con- It will also be notedfrom Figure 1 that the delivery end 42 of the welding conveyer isconnected to the entrant end 43 of the loading conveyer by means of atransfer conveyer 44. In this connection, it will be noted that thetransfer conveyer 44 is shown in Figures 21 to 27, inclusive, and thetransfer conveyer 41 is of the same general construction as the transferconveyer 44 so that it is not believed necessary to illustrate thetransfer conveyer in detail.

In general, it' may be pointed out that the transfer conveyer 41 isadapted to receive, a car-.

riage 38 discharged from the delivery end 39 of the loading conveyer 35and to move this carriage into registration with the entrant end 48 ofthe welding conveyer 36. At the same time, the transfer conveyer 44moves the carriage 38 received from the delivery and 42 of the weldingcontrol unit 68. As pointed out above, this is desirous in that itpermits varying the welding time of the welders in one group withrespect to the welders in the other group so that work of differentthicknesses may be satisfactorily welded.

The carriages 38 on the welding conveyer track 31 are advanced by a stepby step movement to successively position the work on the carriages inregistration with the welders at each of the three stations 46, 41 and48. Upon reference to Figure 2, it will be noted that one carriage 38 ispositioned at each welding station and that each carriage is providedwith a bumper 59 projecting from opposite ends thereof. When thecarriages 38 assume positions on the welding conveyer, the bumpers onthe adjacent ends of conveyer into registration with the entrant end 43of the loading conveyer. In the present instance, the work supported bythe carriage discharged from the delivery end 42 of the welding conveyeris removed from the carriage while the latter is supported on thetransfer conveyer 44 by the unloading device, designated generally inFigure by the reference character 45. As a result, reloading of thecarriages 38 may beinstituted when the carriages assume positions inregistration with the entrant end 43 of the loading conveyer.

Welding conveyer Upon reference to Figure 2, it will be noted that threestations 46, 41 and 48 are supported in spaced relation to each otheralong the welding conveyer track 31. I In the present instance, twogroups of welders 49 and 58 are Supported above the track 31 of thewelding conveyer. The welders are elevated sufficiently to permit freepassage of the carriages 38 beneath the same, and the welders in eachgroup are predeterminedly distributed to weld different parts of thework together. The operation of the welders in the group 49 iscontrolled by a control unit 51, and the operation of the welders in thegroup 58 is controlled by the control unit 52. The purpose of providingtwo control units at the station 46 is to permit varying the weldingperiod of one group of welders so that the parts of the work havingdifferent thicknesses may be satisfactorily welded.

The second station 41 is also provided with two groups of welders 53 and54 also supported directly above the track to permit the carriages 38 topass beneath the same. The two groups of welders 54 are arranged to weldthe work at points spaced from the welds obtained at station 51 and 58are predeterminedly arranged to weldthe work at points spaced from thewelds obtained at both stations 46 and 41. The operation of the group ofwelders 51 is controlled by a control unit 59', and the operation of thegroup of welders 58 is independently controlled by a the carriages, abuteach other, and the bumper 59 on the carriage 33 supported by thetransfer conveyer 41, in registration with the entrant end 48 of thewelding conveyer, engages the bumper on the adjacent end of the carriage38 supported at the first station 46. It follows from the above thatmovement of the carriage 38 on the transfer conveyer 41 in a directiontoward the delivery end 42 of. the welding conveyer effects acorresponding, movement of the carriages supported on the weldingconveyer at stations 46, 41 and 48.

In the present instance, the carriages on the welding conveyer 36 areindexed a distance corresponding substantially to the length of onecarriage by moving the carriage 38 oil the transfer conveyer 41 onto thewelding conveyer track 31 to position the work on this carriage atstation 46. The preceding carriages are, of course, advanced on thewelding conveyer a corresponding distance, and the carriage previouslysupported at the final station 48 is moved onto the transfer conveyer44. In Figures 9 to 12, inclusive, I have illustrated one type ofindexing mechanism that may be employed for the above purpose. Thisindexing mechanism embodies a fluid pressure operated device comprisinga cylinder 68 and a piston 61 reciprocably mounted in the cylinder. Thecylinder 68 is supported beneath the track 31 of the welding conveyerwith its axis extending parallel to the track 31, and the piston 6| isconnected to the rear end of a rack 62 by means of a connecting rod 63.The front end of the rack 62 meshes with a relatively small pinion 64keyed to a drive shaft 65 having the opposite ends journaled in a casing66. As shown in Figure 12, a gear 61 having a diameter substantiallygreater than the diameter of the pinion 64 is also keyed to the driveshaft 65 and meshes with a rack 68. The rack 68 is slidably supported onthe welding conveyer in the manner shown in Figure 10 for movementlongitudinally of the track 31 on the welding conveyer, and the rear endof the rack 68 has a hook 69 secured thereto. It may also be pointed outat this time that the end walls of the casing 66 are slotted to permitextending the racks therethrough, and provision is made in the casingfor guiding the racks. Referring again to Figure 12, it will be notedthat the rack 62 is guided by the downwardly opening channel portion 18of the casing, and the rack 68 is guided by the downwardly openingchannel portion 11.

Upon reference to Figure 9, it will be noted that the length of the rack68 is sufllcient to extend beneath the front end of a carriage 38supported on the'transfer conveyer at the entrant end 48 of the weldingconveyer. The hook 69 on the rear end of the rack 68 is adapted toengage latch members 13 having the upper ends respecdin ' membersrearwardly by the hook 63$ as the rack 68 is moved to its rearwardmostposition. As shown in Figure 11, when the hook 6 is moved by the rack 58rearwardly beyond the lower end of the latch member 13, the latterreturns by gravity to a position at the front side of the hook andengages a block it secured to the forward end of each carriage inadvance of the latch members. The blocks it form abutments for the latchmembers id to prevent forward swinging movement of themembers 33relative to the carriages as the hook 6% is moved forwardly by the rack58. As a result, forward movement of the rack 538 from the positionthereof shown in Figure'9 imparts a corresponding advancing movement tothe carriage 38 on the transfer conveyer it. Due to the abuttingrelationship of the carriage bumpers 59 previously discussed, it followsthat forward movement of the carriage $8 on the transfer conveyer iieifects a corresponding advancing movement of all of the carriages 38 onthe welding conveyer. I

It follows from the above that the indexing rack 68 must be moved adistance corresponding substantially to the length of one of thecarriages 38, and this is accomplished with a relatively short stroke ofthe operating rack 62 by reason of the differential gearing connectingthe rack 52 with the indexing rack GB. It will be apparent uponconsidering Figure 9 that the rack d2 must be moved in the direction ofthe arrow ture for the welding conveyer.

ill to efiect an indexing movement of the rack 68, and this isaccomplished by admitting fluid under pressure into the cylinder 58 atthev rear side of the piston 61!. During this forward movement of thepiston iii in the cylinder 6K3, the

forward-end of the latter is connected to the exhaust so as not tointerfere with the forward movement of the piston. When the piston 65reachesthe end of its forward stroke in the cylinder 6d, the desiredindexing movement of the rack 68 is completed, and the rack 68 isreturned to its rearwardmost position shown in Figure 9 by introducingfluid under pressure into the cylinder til at the front end of thepiston ti. During the rearward movement of the piston 6! in the cylinder66, the rear end of the latter is connected to the exhaust.

Uponreference to Figure 1, it will be. noted that the operation of thepiston 69 is controlled by means of a pair of solenoid operated valves,designated by the reference characters 18 and 19. As will be more fullyhereinafter set forth, when the valve I8 is energized it connects therear end of the cylinder G0 to a source of fluid under pressure, andwhen it is deenergized, it connects the rear end of the cylinder to theexhaust. The valve 19 controls the forward end of the cylinder 60 and isenergized to connect the forward end of the cylinder with a. source offluid under pressure when the valve 18 is deenergized. It will, ofcourse, be understood that the two valves are automatically operated intimed relation to the other instrumentalities of the fixture so as toeffect the indexing movement at the proper interval.

Upon reference to Figures 15, 17 and 18, it will asserts the indexingmechanism is resisted by a plurality of brakes having elongated brakeshoes extending longitudinally of the welding conveyer inpositionspermitting the carriages to move over the shoes. In the presentinstance, one brake shoe is supported at each of the three sta-= tions56, ill and $53 and are yieldably urged into frictional engagement withpressure plates ill secured to the bottom surfaces of the carriages 38by means of springs 62 acting on the bottom surfaces of the shoes 88. Asshown in Figure 17, the springs 82 are spaced from each otherlongitudinally of the brake shoes and are supported by studs 83 with theopposite ends respectively engaging the brake shoes and the frame struc-It will also be observed from Figure 17 that the braking torqueresulting from engagement of the shoes 88 with .the carriages 38 isprevented from moving the shoes in'the direction of advancement of thecarriages by an abutment 8Q depending from each carriage and engageablewith the rear side of a cooperating abutment 85 extending upwardly fromthe welding conveyer framestructure.

Thus, from the foregoing, it will be seen that the shoes 88 exert abraking action on the carriages 38 during the indexing movement thereofand overrunning of the carriages at the end of the indexing movement isresisted. In order to insure stopping of the carriages at the end of theindexing movement thereof, provision is.

thereof extending vertically and the pistons 88 are respectivelyconnected to the forward ends of the brake shoes 80. Fluid underpressure is supplied to the lower ends of the cylinders 31 to move thebrake shoes upwardly into engagement with the carriages 38 by a solenoidactuated valve 89 (Figure 1) movable to its open position at the end ofthe indexing movement of the carriages by energizing the solenoidassociated with the valve in a manner to be more fully hereinafterdescribed. As will also be set forth below, the solenoid is deenergizedafter the carriages 3B are arrested by the brake shoes 8G and the valve89 exhausts the lower ends of the cylinders 81 to permit return movementof the pistons 89.

At theend of the indexing movement of the carriages 38, the threecarriages at the welding stations 46, 41 and 48 are raised off the track31 to register the work on the carriages with the welders byliftingdevices 90 having elevating plungers 9! engageable with the undersidesof the carriages. Upon reference to Figure 15, it will be noted that theupper ends .of the plungers 9! are engageable in sockets 92 mountedon-the,

undersides of the carriages 38. It follows, therefore, that thecarriages 38 must be positioned at the end of each indexing movementwith the sockets 92 in alignment with the upper ends of theplungers 9!.For accomplishing the above result, I provide a latch 93, shown inFigure 19, as comprising a latch arm 94 and a fluid pressure device 95for operating the arm 94. The latch arm 94 'is pivoted at its rear endon the frame. structure of the welding conveyer and is provided with ahook 96 at the forward end movable into the path of travel of thecarriages 38 by the device 95. The latch 93 is positioned adjacent thedelivery end 42 of the welding conveyer 36 and the hook 96 at theswinging end of the latch arm 04 engages the rear end of the carriage atthe final welding station 08. The construction is such that the hook 96forms a positive stop for the carriages on the welding conveyer andpositions the latter carriages with the sockets 02 in registration withthe upper ends of the elevating plungers 9|.

The latch arm 94 is swung upwardly to position the hook in operativerelation to the forwardmost' carriage on the welding conveyer by thefluid pressure operated device 95 during the interval the carriagesapproach the end of their indexing movement. Referring again to Figure19, the device 95 comprises a cylinder 01 and a piston 98 reciprocablymounted in .the cylinder. The opposite ends of the cylinder 91communicate with a solenoid operated valve 99 which is energized intimed relation to the indexing movement of the carriages 38 to connectthe lower end of the cylinder 91 to a source of fluid under pressure andto connect the opposite end of the cylinder to the exhaust. As a result,the piston 98 is moved in an upward direction in the cylinder 9t and thelatch arm 94 is swung in a corresponding direction by the piston 98 to'locate the stop in the path of advancement of the carriages. After thelatch 93 serves its purpose, the solenoid operated valve is'deenergizedand the operation of the device 05 is reversed to move the latch arm 9dout of the path of travel of the carriages. The manner in which thesolenoid oper ated valve 95? is controlled will be set forth more indetail in the following description.

After the carriages 38 are indexed along the welding conveyer and thelatch 93 is operated to position th carriages 33 relative to theelevating plungers d, the latter are raised to engage the upper endsthereof in the sockets 92 on the carriages and lift the carriages at theWelding stations it, ll and 48 toward the welders. As shown in Figures 2and 15, six lifting devices 90 are provided at each of the threestations 46, 4i and it. The six lifting devices 90 at each weldingstation are positioned so that three lifting devices are positioned ateach side of the registering carriage 38 and are spaced from each otherlongitudinally of the welding conveyer so as to engage the carriage atpoints adjacent opposite ends and at points intermediate the ends. Itwill also be noted that the lifting devices 90 at one side of thewelding conveyer are positioned directly opposite the lifting devices atthe opposite side of the latter conveyer and, accordingly, it may besaid that the lifting devices are arranged in pairs with the devices ofeach pair positioned directly opposite each other.

Referring again to Figure 15, it will be noted that the lifting devicesof each pair are operatively connected by means of a transverse shaftI00 supported intermediate the ends by 2. casing IM and having theopposite end portions journaled in bearings formed in the housings I02of the lifting devices. Secured to each end of each of the transverseshafts I00 is a pinion I03 located in the housings I02 and meshing withrack teeth formed on the elevating plungers 9I. As shown in Figure 16,the plungers are mounted in the housings I02 for vertical slidingmovement and the plungers 9I of each pair of lifting devices areoperated by rotating the transverse shafts I00. In the present instance,the shafts I00 are rotated in one direction to simul .taneously raisethe plungers 9I at each welding station and are rotated in the oppositedirection to simultaneously lower the plungers 9|.

For rotating the shafts I00, a pinion I04 is rotatably mounted in eachhousing IM and is secured to the shaft I00 extending through the latterhousing. The housings IOI are secured to the frame structure of thewelding conveyer in alignment with each other and are provided withguide channels I05 for 'slidably supporting 'a sectional rack I06 in aposition to mesh with ton I09 reciprocably mounted in the cylinder.

The piston I09 is provided ith a rod H0 extending through the front endof the cylinder I08 and connected at its forward end to a cross head II!intermediate the ends of the latter. The opposite ends of the cross headare connected to a second cross head H2 at the rear end of the device mlby rods l 33 extending along opposite sides of the cylinder H153. Thesecond cross head HI, in turn, is connected to the forward end of thereels so that forward movement of the piston ltd moves the rack in a corresponding direction to raise the elevating plungers 9i, and rearwardmovement of the piston I09 operates the reel; to lower the elevatingplungers.

The opposite ends of the cylinder MS are alternately connected to asource of fluid under pressure and to an exhaust by a pair of solenoidoperated. valves M 3 and H5, diagrammatically shown in Figme i. Thevalve lid controls the rear end of the cylinder 5 and the valvelitcontrols the front end of the cylinder. The ar rangement is such thatwhen the valve lid is energized it supplies fluid under pressure to therear end of the cylinder and moves the racl: I06forwardly to raise theplungers 98 of the elevating devices During this interval, the forwardend of the cylinder I08 is connected to the exhaust and remains in thisposition untii the work has been welded. Upon completion of the weldingoperation, the solenoid valve lid is operated to exhaust the rear end ofthe cylinder I 08 and the solenoid valve H5 is energized to connect theforward end of the cylinder ltd to the source of fluid under pressure.As a resuit, the elevating plungers are lowered and the carriages 38 arereturned to positions on the tracks 31 of the welding conveyer. Themanner.

in which the solenoid operated valves H4 and I I5 are operated in propertimed relation to each other and to the remaining instrumentalities ofthe fixture will be fully described in connection with the operation ofthe fixture.

Welder control units clamped against a plurality of electrodes H8 fixed.to the carriages in positions directly opposite the electrodes on thewelders to be presently described. In the present instance, a pluralityof clamps are provided for accomplishing the above result, and one ofthese clamps is designated in Figure 20 by the reference character Ill.The clamps III are secured to the-superstructure I I8 of. the weldingconveyer frame, and each clamp-is provided with a head 8- adapted toengage a part of the work.v It will be observed from Figure 20 that theheads II8 of the clamps are supported for vertical sliding movement andare normally yieldably urged in'to clamping engagement with the work bymeans of springs I20. r

The electrodes IIG are grounded on the carriages 38, and the carriagesare connected in the welding circuit by means of electrical contactmembers I 2! secured at their lower ends to the carriages in alignmentwith suitable I connected to the arm through the medium of resockets I22depending from the superstructure N8 of the welding conveyer frame. Thesockets I22 are connected in the welding circuit by means of a jumperI23. The above construction is such that when the carriages 38 areraised to their uppermost positions by the lifting devices 80, the workon the respective carriages is clamped against the carriage electrodesII 6 bythe clamps Ill, and the electrical contact members I2I on thecarriages engage in the sockets I22 toconnect the electrodes [I8 in thewelding circuit.

'As stated above, each group of welders at the several welding stationsis independently controlled by a control unit. One of the control unitsis shown in Figures 3 to 5, inclusive,'and comprises a distributingvalve I24. Upon reference to Figure 3, it will be noted that thedistributing valve I24 includes a plate I25 having aplurality ofcir-cumferentially spaced radially extending passages I26 in theperipheral .portion thereof. The outer end of each passage I20communicates with a distributing conduit I21 and the latter, in turn,communicates with a plurality of welders I28. Each welder I 28 isprovided with a cylinder I29 and a piston I30 reciprocably' mounted inthe cylinder. In the present instance, the upper end of the cylindercommunicates with the distributing passage I21, and the piston I30 ismoved downwardly relative to the cylinder by the action of the fluidpressure admitted to the upper end of the cylinder through thedistributing conduit I21. Downward movement of the piston in thecylinder is resisted by means of a spring I3I so that when the cylinderis exhausted the piston will be returned to its uppermost-position bythe spring. The piston I30 is operatively connected to an electrode I32by means of a plunger. I33 in such a manner that when fiuid pressure isadmitted to the upper end of the cylinder I28, the electrode I32cooperates with the registering electrode I I8 to clamp the worktherebetween.

Fluid under pressure is supplied to the distributingconduits I2I- by arotatable arm I34 having a passage I35 therethrough and sup- .ported forrotation beneath the plate I25. The lower end of the passage I35communicates with a source of hydraulic fluid medium under presductiongearing I38. Upon reference to Figure it will be noted that the electricmotor I38 for' each control unit is arranged in an independent circuitI38 with a switch I40. Although the switches I48 are diagrammaticallyillustrated in Figure 2as being located adjacent the electric motor I38.nevertheless, in the actual construction these switches are in the formof normally open limit switches and are positioned to be closed by thecarriages 38 as they are raised by the elevating devices 88.

It follows from the above that when the carriages are raised ofl of thewelding conveyer, the

switches I40 are closed so that by the tim the work at the severalwelding stations is supported in registration withthe electrodes I32 ofthe welders I28, the distributing arm I34 of each control unit isrotated. As the distributing arm I34 rotates, hydraulic fluid medium issuccessively introduced into the welders I28 of each group, and theelectrodes I 32 of the respective welder are moved downwardly tocooperate with the electrodes II 8 to clamp the work therebetween. Afterthe electrodes I32 of the several groups of welders are moved downwardlyinto engagement with the work, the welding circuits are closed to efiectthe desired welds. In the present instance, each welder control unitcomprises a switch I, and this switch closes and opens the weldingcircuit during the interval each distributing conduit I27 is connectedto the source of hydraulic fluid medium. In other words, only one switchI4! is provided for each control unit.

in the welding circuit. The contact member I44 is moved into engagementwith the contacts I45 by means of air under pressure supplied to theswitch closing chamber I48, and the contact member I44 is moved out ofengagement with the stationary contacts I45 by means of air undernfissure supplied to the switch opening chamber Upon reference to Figure5, it will be noted that the switch closing chamber I48 communicateswith the pneumatic pressure supply line I42 through the medium of aconduit I48 and that a valve I48 controls communication through thepassage I48. The valve I48 is in the form of a piston having an annulargroove I50 extending around the periphery thereof and adapted toestablish: communication between the supply line I42 and the passage I48when the valve pistonis moved to its forwardmost position (shown inFigure 5). r The valve piston I48 is moved to its i'orwardmost-positionby a rotatable operating sure, and the upper end of the passage I35 suc-Q cessively communicates with the inner ends of disc I50 connected tothe distributing arm I34 of each unit for rotation with the distributingarm; Upon reference to Figure 4, it will be noted that a plurality ofcircumferentially, spaced cams I5l extend radially outwardly from theperiphery of the disc I50 and successively operate to move the valvepiston I48 to its open position through the medium of a lever I52. Thelever I52 is rockably supported onthe control unit and is successivelyoperated by the cams I 5I to move the valve piston I48 in a forwarddirection to the

